Abstract: A reflecting surface is formed at the utmost end of a smaller diameter wire rod, and the utmost end portion thereof is inserted into a small hole to image the internal surface thereof. A laser beam is incident on the reflecting surface and impinged on the internal surface of the small hole while rotating the smaller diameter wire rod inserted into the small hole around the axis of the smaller diameter wire rod and relatively to the small hole. The laser beam reflected from the internal surface of the small hole and subsequently the reflecting surface is reflected by a half-silvered mirror provided in the way of an optical path of the laser beam and guided to an image processor. The condition of the small hole is observed by the image processor. Thereby the condition of the internal surface of the small hole is observed without breaking down an inspected object.